1. Field of Invention
This invention relates to nozzles for spraying a resin. More particularly, it refers to a nozzle containing an air assist for reducing resin loss between the nozzle and a mold surface and providing for a more evenly spread mixture of resin and glass on the mold surface.
2. Description of the Prior Art
Recently, the fiberglass reinforced plastics (FRP) industry has come under close scrutiny of local, state and federal officials concerning emissions of volatile organic compounds (VOCs), including but not limited to emission of evaporated Styrene. As is well known, Styrene is a major component in the polyester resin that is widely used throughout the FRP industry and, in most resin applications, Styrene may encompass as much as 45%, by volume, of the entire polyester resin formula.
In the FRP industry, it has become customary to apply fiberglass reinforced plastics using spray equipment to apply the resin to mold surfaces. Examples of products manufactured in this manner include showers and bathtubs, boat hulls, recreational vehicles and various construction materials. As a volatile organic compound, Styrene will gradually evaporate from an open container without outside stimulus. When a resin mixture including Styrene is sprayed, the rate of evaporation drastically increases. Recent studies sponsored by the Environmental Protection Agency have shown that when a resin containing Styrene is sprayed, especially in the "lay-up" process, it can emit as much as 22 to 23% of its total Styrene content in the form of evaporation. As such, in an effort to reduce such emissions in the workplace, which may be damaging to the health of workers and to the public in general, the FRP industry needs to take steps to reduce such emissions.
Customarily, when fiberglass reinforced plastic products are manufactured, the resin is sprayed and chopped fiberglass is introduced into the spray pattern of resin beyond the resin nozzle so that a resin/glass matrix is deposited on the mold surfaces. As is known, the fiberglass addition is a critical part of the application because it provides the necessary reinforcement to build the fiberglass part. Spray guns have been developed which combine dispensing of resin with mixing, therein, of chopped fiberglass beyond the resin nozzle. Such a gun, known in the art as a "chopper gun" has greatly advanced the speed and efficiency with which FRP parts are manufactured.
When the resin is atomized into fine droplets by the dispensing nozzle, the surface area of the resin that is exposed to the atmosphere is greatly increased and, correspondingly, evaporative Styrene loss greatly increases as well. To solve this problem, chopper guns are now manufactured incorporating a nozzle referred to as a "FLOCOATER". Such a "FLOCOATER" nozzle is specifically designed with a multiplicity of small holes having diameters in the range of 0.010 to 0.035 inches and arranged in a desired pattern. Such a nozzle projects resin out of these holes in a showering or sprinkling fashion rather than in a spraying fashion. Use of a "FLOCOATER" nozzle reduces evaporative loss of Styrene to as low as 4 to 5%, by volume, thereof. This reduction is a great improvement over the prior art.
However, while the use of a "FLOCOATER" nozzle greatly reduces Styrene emissions, chopper guns employing "FLOCOATER" nozzles have not yet been perfected because the chopped fiberglass is not uniformly distributed within the resin stream beyond the resin nozzle. This non-uniform distribution of chopped fiberglass in the resin stream results in a non-uniformity of distribution of the fiberglass within the resin as deposited on the mold surfaces. The resulting laminate formed from the non-uniform distribution of chopped fiberglass suffers significant loss of physical strengths, especially in the flexural and tensile areas. Additionally, if the fiberglass does not distribute evenly throughout the spray pattern, "dry spots" (a lack of glass saturation) can be formed on the mold surface. Such results are unacceptable, causing the part or product to be rejected, thereby causing economic waste.
Other problems exist as well. The required velocity of the fiberglass dispensed from the source thereof, as attached to the chopper gun, causes as much as 30% or more of the chopped fiberglass to simply fall through the resin stream and wind up on the adjacent floor surface as waste material. This is a result of the fiberglass falling through small gaps between the resin streams inherent with the emerging stream pattern. Such waste can be an environmental hazard as well as cause significant economic waste.
As such, a need has developed for a new chopper gun design permitting uniform distribution of chopped fiberglass within the resin stream while reducing wastage of chopped fiberglass.
The following prior art is known to Applicant:
U.S. Pat. No. 4,635,852 to Muhlnickel, Jr.; PA1 U.S. Pat. No. 4,824,017 to Mansfield; PA1 U.S. Pat. No. 4,854,504 to Hedger, Jr. et al.; PA1 U.S. Pat. No. 4,967,956 to Mansfield; PA1 U.S. Pat. No. 5,046,668 to Ikeuchi et al.; PA1 U.S. Pat. No. 5,080,283 to Kukesh et al.; and PA1 U.S. Pat. No. 5,178,326 to Kukesh et al. PA1 (A) The present invention provides a drastic improvement over a conventional "FLOCOATER"-type chopper gun, wherein resin is supplied to an outlet nozzle which, if a "FLOCOATER" configuration is employed, consists of a plurality of small diameter holes, in the range of 0.010 to 0.035 inches in diameter arranged in a pattern and so sized to cause resin to flow therethrough in a manner similar to the operation of a shower or sprinkler rather than that of a spraying device. PA1 (B) The chopper gun also includes a source of chopped fiberglass having an outlet nozzle positioned to spray the chopped fiberglass over the resin flow so that the chopped fiberglass mixes with the resin flow before being deposited on mold surfaces. PA1 (C) An air assist is provided designed to spray an air knife or sheet of air outwardly therefrom intersecting the resin streams at a point forward of the nozzle, blending the streams together to form a uniform spray pattern, thereby permitting chopped reinforcing fibers to fall into the resin streams from an opposed side from that of the air assist, thereby further permitting the reinforcing fibers to blend uniformly within the resin spray. PA1 (D) In the preferred embodiment of the present invention, the air assist consists of a generally elliptical slot located on a generally conical nozzle body that protrudes slightly beyond and below the resin nozzle and is slightly upwardly angled.
Although some references in the prior art teach the use of an air stream, they show the air stream positioned parallel to the resin streams. When the air stream is introduced in this manner, between the resin stream and the falling chopped fiberglass, additional problems are created. For instance, the air stream actually carries and blows the chopped fiberglass downstream, prohibiting the reinforcing fibers to blend within the resin stream. Such is shown in Kukesh et al. '283 wherein the chopped reinforcing fibers do not mix with the resin until both the resin and reinforcing fibers make contact with the substrate to be sprayed (see FIG. 1--Kukesh et al. '283). The present invention differs from the teachings of the prior art as contemplating the use of an air nozzle positioned below the resin nozzle and angled slightly upwardly. The air nozzle is specifically designed to blend the resin streams to promote uniform distribution of chopped fiberglass within the resin stream before the stream reaches the mold surface.